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Mapping the Distribution of Maritime Chaparral Species in the Monterey Bay Area Prepared for the U. S. Fish and Wildlife Service, Ventura Fish and Wildlife Office Eric Van Dyke and Karen Holl April 26, 2003 Introduction Central maritime chaparral is an uncommon vegetation type that is present in patches at locations scattered throughout the Monterey Bay region. Maritime chaparral stands are dominated by one or more Arctostaphylos taxa, including several subspecies of burl forming A. tomentosa (woollyleaf, shaggy-barked, or brittleleaf manzanita) and four locally endemic, non-burl forming species that were the primary focus of this study: A. hookeri ssp. hookeri (Hooker’s manzanita), A. pajaroensis (Pajaro manzanita), A. montereyensis (Monterey or Toro manzanita), and A. pumila (sandmat manzanita). At some locations, stand dominance is shared with Adenostoma fasciculatum. Several State and Federally listed species are associated with central maritime chaparral, including Chorizanthe pungens var. pungens, Cordylanthus rigidus ssp. littoralis, and Piperia yadonii. Our understanding of the distribution of Monterey Bay maritime chaparral and its endemic shrubs is largely due to the work of Jim Griffin in the 1970s (Griffin 1978). The occurrence of maritime chaparral is typically associated with dry, well-drained soils or exposed upland locations. Several species present in maritime chaparral, including Dendromecon rigida, Pickeringia montana, and Quercus wislizenii, are typical of much drier inland habitats. Two Monterey Bay endemic shrubs, Arctostaphylos pajaroensis in the Prunedale region and A. pumila at former Fort Ord and the nearby Monterey Airport area, are almost entirely restricted to ancient dune sands. In the Prunedale sandhills, discrete chaparral patches occur within a matrix of coast live oak woodland. The Monterey Bay area’s largest maritime chaparral expanses are found on rolling sandhills at central and southwestern Fort Ord. At more inland locations, from eastern Fort Ord through Toro Park and the Pine Canyon area, scattered individuals and occasional patches of the uncommon endemic A. montereyensis occur on heavier soils within expanses of Adenostoma chaparral and shrubland. Arctostaphylos hookeri ssp. hookeri, another uncommon Monterey Bay area endemic, inhabits a variety of coastal chaparral habitats—from exposed sandstone crags in the Prunedale area to heavy clay soils in the closed-cone conifer forest understory of the Del Monte Forest. Maritime chaparral is threatened by fragmentation due to agricultural and residential development, poor recruitment resulting from wildfire suppression, successional transition to oak woodland or closed-cone conifer forest, and invasion by exotic species such as Carpobrotus edulis, Cortaderia jubata, Eucalyptus globulus, and Genista monspessulana. The objective of this project was to map the boundaries of central maritime chaparral patches in the Monterey Bay area and to compile abundance data for the region’s endemic Arctostaphylos species. Presence data for Ceanothus cuneatus var. rigidus and 1 Ericameria fasciculata, two maritime chaparral-associated local endemics, were also compiled as encountered. The four Arctostaphylos species and Ericameria fasciculata are considered rare, threatened, or endangered (List 1B) by the California Native Plant Society; Ceanothus cuneatus var. rigidus is on the CNPS watch list (List 4). High-resolution aerial imagery was interpreted to map the distribution of chaparral patches. A limited set of field surveys, using Griffin’s sampling techniques to facilitate comparison with earlier studies, were undertaken as ground truth for the image interpretation process and to develop abundance estimates for the six target species. The results of this survey are available as a set of ArcView GIS layers on the accompanying CD. Methods Maritime Chaparral Mapping Griffin’s original 1978 distribution map of Monterey Bay area endemic shrubs was located in the files at Hastings Reserve. We scanned and georectified this map to serve as our starting point for mapping the region’s maritime chaparral stands (Figure 1). The extent of maritime chaparral was determined through aerial image interpretation techniques. A variety of flight dates and types of aerial imagery were reviewed to determine which was most suitable for distinguishing chaparral habitat. After color enhancement of the selected photographs to emphasize habitat distinctions, we performed systematic searches in the vicinity of each of Griffin’s designated chaparral “localities”. Additional sites that were identified as maritime chaparral by local experts or from voucher specimens were also searched. Identified chaparral patches were re-located and digitized directly from high- resolution digital ortho images to ArcView polygon shapefiles. This methodology assured consistent spatial accuracy and a common timeframe. All Monterey County localities, with the exception of a relatively small area south of Gibson Canyon, were digitized from Monterey County’s December 1999 0.6 m/pixel panchromatic DOQs (HAW 1999). Digitizing of the Santa Cruz County localities at Buena Vista and Calabasas was completed using Monterey County’s May 2001 0.6 m/pixel color infrared DOQs (HAW 2001). Coverage for southern Gibson Canyon, which is not yet available from Monterey County’s digital ortho series, was from 1993 U. S. Geological Survey 1.0 m/pixel panchromatic DOQs (NAPP 1996). Heads-up digitizing was performed at a standard scale of 1:4000, yielding chaparral polygons with approximately 10 m spatial accuracy and a minimum mapping unit of approximately 2500 m2 (although a number of smaller polygons that could be clearly identified were also included). Interpretation of aerial imagery is effective where textural differences between habitat types are visually distinctive. Boundaries between maritime chaparral patches and adjacent woodland, grassland, and developed areas are typically abrupt and were readily identified on our imagery. The project’s two contributors independently digitized several test patches at widely distributed locations to assess the level of inconsistency of interpretation; the resulting chaparral acreage was nearly identical in all cases. In areas of transition from chaparral to other habitat types, the visual threshold was approximately 50% shrub cover. Therefore predominately woodland or grassland 2 regions where chaparral associated shrubs were present could not be identified in this study. Chaparral and sage scrub habitats were occasionally visually ambiguous. Inspection of color or color infrared imagery usually resolved these interpretation questions, although field visits were occasionally required. A paved road was always considered to be the boundary of a chaparral patch, as were cleared areas wider than approximately 20 m. Unpaved roads and paths were generally included within chaparral polygons, as were areas of disturbance, bare ground, and fragments of other habitat types provided they were smaller than the minimum mapping unit. The chaparral polygons delineated by our mapping methodology correspond closely to the Woollyleaf manzanita series defined in the California Native Plant Society’s Manual of California Vegetation (Sawyer and Keeler-Wolf 1995), i.e. a continuous canopy dominated by manzanita and other broad-leaved evergreen shrubs that occurs on upland bluffs, dunes, mesas, outcrops, slopes, and terraces. Figure 2 shows an example of digitized chaparral polygons over the ortho imagery. Distribution and Dominance of Endemic Shrubs The presence and estimated density of endemic Arctostaphylos species, Ceanothus cuneatus var. rigidus, and Ericameria fasciculata in or near the mapped chaparral stands were determined from targeted field surveys and through a review of the California Natural Diversity Database (CNDDB 2002), voucher records at the Pacific Grove Museum of Natural History herbarium, and through interviews with local experts. Only voucher records collected since 1977 (subsequent to Griffin’s field work) were included. Field visits were made to parklands and protected conservation lands and other readily accessible sites where maritime chaparral was present. Ten meter by ten meter square sampling plots were selected in undisturbed portions of the chaparral and dominance of the six target species was estimated according to the Braun-Blanquet minimal-area relevé method (Mueller-Dombois and Ellenberg 1974, Griffin 1978, Van Dyke et al. 2001). Occurrences of the six target species that were observed outside of these sampling plots, and an estimate of their relative density, were also recorded. Estimated species abundance at former Fort Ord was obtained by scanning, georectifying, and digitizing published distribution maps (USACE/Jones & Stokes 1992). Results and Discussion Maritime Chaparral Mapping Interpretation of high-resolution imagery allowed us to identify and digitize about 17,600 acres of chaparral throughout the study area (Table 1; Figure 3). The resulting dataset, which comprises 654 polygons, is included in the accompanying data CD as the ArcView shapefile “chaparral.shp”. (The contents of the CD are listed in Appendix 1.) The chaparral that we mapped consists of three distinct habitat types: · Maritime chaparral. Central maritime chaparral is dominated by Arctostaphylos species, typically one or more varieties of A. tomentosa in combination with one or more local endemic Arctostaphylos species. Adenostoma fasciculatum is frequently present, but rarely dominant.

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